Digital lighting technologies, i.e. illumination based on semiconductor light sources, such as light-emitting diodes (LEDs), offer a viable alternative to traditional fluorescent, HID, and incandescent lamps. Functional advantages and benefits of LEDs include high energy conversion and optical efficiency, durability, lower operating costs, and many others. Recent advances in LED technology have provided efficient and robust full-spectrum lighting sources that enable a variety of lighting effects in many applications. Some of the fixtures embodying these sources feature a lighting module, including one or more LEDs capable of producing different colors, e.g. red, green, and blue, as well as a processor for independently controlling the output of the LEDs in order to generate a variety of colors and color-changing lighting effects, for example, as discussed in detail in U.S. Pat. Nos. 6,016,038 and 6,211,626.
In particular, luminaires employing high-flux LEDs are fast emerging as a superior alternative to conventional light fixtures because of their higher overall luminous efficacy and ability to generate various lighting patterns and effects. One significant concern in the design and operation of these luminaires is thermal management, because the LEDs perform at a higher efficacy and last longer when run at cooler temperatures. High-flux LEDs tend to be particularly sensitive to operating temperatures, as the efficiency of dissipating heat generated by these LEDs significantly correlates to the operating life, performance, and reliability of the LED light source. Thus, maintaining optimal junction temperature is an important consideration in developing a high-performance lighting system. Efficient heat dissipation, however, may present a challenge when the size of the fixture and the density and flux of the LED light sources increase. Also of concern for larger fixtures, such as those used for exterior applications, are safety of handling and installation as well as ruggedness.
One desirable application for LED-based luminaires, particularly those employing high-flux LEDs, is illumination of large architectural surfaces and objects, concentrating light in a specific direction. Conventional projection fixtures have been used for this purpose for many years in various theatrical, television, architectural and general illumination applications (e.g., overhead projection, spotlight illumination, illumination of airport runways and high-rise buildings, etc.). Typically, these fixtures include an incandescent or a gas-discharge lamp mounted adjacent to a concave reflector, which reflects light through a lens assembly to project a narrow beam of light over considerable distance towards a target object.
In recent years, LED-based lighting fixtures also have been used in some types of projection lighting fixtures, configured as luminaires for interior or exterior applications to improve definition of three-dimensional objects, as well as provide spotlight illumination or wall-washing lighting effects for architectural surfaces. In particular, surface mount or chip-on-board assemblies of single or multiple LEDs have attracted attention in the industry for use in applications requiring high luminance combined with narrow-beam light generation (to provide tight focusing/low geometric spreading of illumination). A “chip-on-board” (COB) LED assembly refers generally to one or more semiconductor chips (or “dies”) in which one or more LED junctions are fabricated, wherein the chip(s) is/are mounted (e.g., adhered) directly to a printed circuit board (PCB). The chip(s) is/are then wire bonded to the PCB, after which a glob of epoxy or plastic may be used to cover the chip(s) and wire connections. One or more such LED assemblies, or “LED packages,” in turn may be mounted to a common mounting board or substrate of a lighting fixture.
For some narrow-beam applications involving LED chips or dies, optical elements may be used together with the LED chip-on-board assembly to facilitate focusing of the generated light to create a narrow-beam of collimated or quasi-collimated light. Optical structures for collimating visible light, often referred to as “collimator lenses” or “collimators,” are known in the art. These structures capture and redirect light emitted by a light source to improve its directionality. One such collimator is a total internal reflection (“TIR”) collimator. A TIR collimator includes a reflective inner surface that is positioned to capture much of the light emitted by a light source subtended by the collimator. The reflective surface of conventional TIR collimators is typically conical, that is, derived from a parabolic, elliptical, or hyperbolic curve.
Thus, there exists a need in the art for a high-performance LED-based luminaire with improved light extraction and heat dissipation properties. Particularly desirable is an LED-based narrow-beam luminaire suitable for large scale lighting applications, such as spotlight illumination of large objects and structures or wall-washing lighting effects for exterior architectural surfaces.